Electro-hydrodynamic wind energy system

ABSTRACT

A system for electro-hydrodynamically extracting energy from wind includes an upstream collector that is biased at an electric potential and induces an electric field. An injector introduces a particle into the electric field. The wind drag on the particle is at least partially opposed by a force of the electric field on the particle. A sensor monitors an ambient atmospheric condition, and a controller changes a parameter of the injector in response to a change in the atmospheric condition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. ProvisionalPatent Application Ser. No. 61/011,701, filed on Jan. 22, 2008 by DavidCarmein; U.S. Provisional Patent Application Ser. No. 61/066,650, filedon Feb. 22, 2008 by David Carmein; and U.S. Provisional PatentApplication Ser. No. 61/199,598, filed on Nov. 18, 2008 by David Carmeinand Dawn White, each entitled Electro-Hydrodynamic Wind Energy Systemand each of which are hereby incorporated herein by reference in theirentirety.

TECHNICAL FIELD

In various embodiments, the present invention relates to systems andmethods for electro-hydrodynamic wind energy and, more specifically,converting wind energy directly into electrical energy.

BACKGROUND

Electro-hydrodynamic (“EHD”) wind energy conversion (“WEC”) is a processwherein electrical energy is extracted directly from wind energy. Justas flakes of snow may be driven by the wind to create a “current” ofsnowflakes, so too may wind be hydrodynamically coupled to chargedspecies to create a true electrical current in free space. The generatedcurrent may be connected to an electrical circuit by means of anelectrostatic field to perform useful work.

EHD systems exhibit a number of advantages over conventional windturbines. For example, conventional wind turbines have a maximumallowable wind speed beyond which their blades, mechanical components,and electrical generating equipment may be damaged. Once this maximumwind speed, or “cut-out” speed, is reached, the wind turbine's bladesmay begin to furl in order to avoid damage to the turbine. Typicalcut-out speeds for small turbines are approximately 28 mph (12.5 m/s).Medium and large turbines may cut out at approximately 60 mph (26.8m/s).

EHD systems, however, are solid-state devices, with no rotatingmachinery, shafts, bearings, gears, lubrication oil, brakes, equipmenthousing, and the like. Thus, EHD systems have no furling speed, and maycontinue to generate energy from wind even at high wind velocities.Furthermore, even though some large conventional turbines may have ahigh furling speed, conventional turbines may not produce more thantheir rated power. Consequently, their power curve is substantially flatabove the furling speed, whereas EHD power continues to rise withincreasing wind velocity.

At low or medium wind velocities, however, traditional EHD systems areinefficient, and may not generate as much energy as it takes to runthem. For example, EHD systems require energy to create the chargedspecies and, in the case of liquid-based charge carriers, energy to pumpthe liquid and hydraulically pressure spray it to create small diameterparticles. Furthermore, traditional EHD systems are expensive, and maynot be cost-effective at any wind velocity.

Clearly, a need exists for a cost-effective EHD system that is capableof generating net positive energy at a wide range of wind velocities.

SUMMARY

Embodiments of the present invention include systems and methods forincreasing the efficiency of EHD systems while simultaneously loweringtheir cost. For example, a control system may be used to monitor ambientenvironmental conditions such as wind speed, wind direction,temperature, and humidity, and adjust parameters of the EHD in responseto increase or maximize the energy extracted from the wind. In certainembodiments, various diffusers and/or airfoils may be used to increasethe ambient wind velocity. Alternatively or additionally, MEMS devicesmay be used to create charged particles more efficiently thantraditional means. Various applications may place the EHD systems inareas of consistently high wind speed, such as at high altitudes.

In general, in one aspect, a system for electro-hydrodynamicallyextracting energy from wind includes, an upstream collector biased at anelectric potential. The electric potential induces an electric field,and an injector introduces a particle into the electric field. Wind dragon the particle is at least partially opposed by a force of the electricfield on the particle. A sensor monitors an ambient atmosphericcondition, and a controller changes a parameter of the system inresponse to a change in the atmospheric condition.

One or more of the following features may be included. The particle maycarry an electric charge. The atmospheric condition may be ambient windspeed, temperature, pressure, and/or humidity. The parameter of thesystem may be particle size, electric charge per particle, particle flowrate, electric potential, electric field strength, and/or a separationbetween the upstream collector and electrical ground.

The system may further include a downstream collector, which may belarger than the upstream collector. The particle may be a droplet of aliquid, and may include a solid particle and/or a low-volatility liquid.The injector may be an electrospray injector, and may include a Taylorcone, a MEMS device, a metal needle, a plastic needle, plastic tubing,and/or a dielectric-barrier discharge device. The particle may be anion.

The system may further include a shaped structure for increasing windspeed within the electric field. The controller may respond to changesin the atmospheric condition in real time.

In general, in another aspect, a method for electro-hydrodynamicallyextracting energy from wind begins with the step of biasing an upstreamcollector at an electric potential. The electric potential induces anelectric field, and particles are injected into the electric field. Winddrag on the particles is at least partially opposed by a force of theelectric field on the particles. An ambient atmospheric condition ismonitored, and a parameter related to at least one of the particles andthe electric field is changed in response to a change in the atmosphericcondition.

One or more of the following features may be included. The atmosphericcondition may be ambient wind speed, temperature, pressure, and/orhumidity. The parameter may be particle size, electric charge perparticle, particle flow rate, electric potential, electric fieldstrength, and/or a separation between the upstream collector andelectrical ground.

The particles may be collected with a downstream collector. Eachparticle may be a droplet of a liquid and the step of injecting mayinclude injecting the droplet with an electrospray injector. The dropletof liquid may include a solid particle and/or a low-volatility liquid.The step of injecting may further include forming a Taylor cone. Windspeed may be increased within the electric field. The step of changingthe parameter may occur in real time.

These and other objects, along with advantages and features of thepresent invention herein disclosed, will become more apparent throughreference to the following description, the accompanying drawings, andthe claims. Furthermore, it is to be understood that the features of thevarious embodiments described herein are not mutually exclusive and mayexist in various combinations and permutations.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of various aspects and embodiments of theinvention can be better understood with reference to the schematicdrawings described below, and the claims. The drawings are notnecessarily to scale, emphasis instead generally being placed onillustrating the principles of the invention. In the drawings, likereference characters generally refer to the same parts throughout thedifferent views. In the following description, various embodiments ofthe present invention are described with reference to the followingdrawings, in which:

FIGS. 1-4 illustrate EHD systems in accordance with embodiments of theinvention;

FIGS. 5-7B illustrate diffusion bodies in accordance with embodiments ofthe invention;

FIGS. 8-10 illustrate nozzle configurations in accordance withembodiments of the invention;

FIGS. 11-12 illustrate EHD extrusion bodies in accordance withembodiments of the invention;

FIGS. 13-14 illustrate nozzle configurations in EHD extrusion bodies inaccordance with embodiments of the invention;

FIG. 15 illustrates an EHD louver in accordance with one embodiment ofthe invention;

FIGS. 16-19 illustrate EHD louver arrays in accordance with embodimentsof the invention;

FIG. 20 illustrates a staggered EHD louver array in accordance with oneembodiment of the invention;

FIG. 21 illustrates an asymmetric EHD electrode in accordance with oneembodiment of the invention;

FIG. 22 illustrates a ground-based EHD system in accordance with oneembodiment of the invention;

FIG. 23 illustrates a tower-mounted EHD system in accordance with oneembodiment of the invention;

FIG. 24 illustrates a building-mounted EHD system in accordance with oneembodiment of the invention;

FIG. 25 illustrates an airfoil-mounted EHD system in accordance with oneembodiment of the invention;

FIGS. 26A-30 illustrate lighter-than-air EHD systems in accordance withembodiments of the invention; and

FIGS. 31A-31B illustrate a wind-shear-based airfoil-mounted EHD systemin accordance with one embodiment of the invention.

DETAILED DESCRIPTION

A basic principle of an EHD system involves using wind energy to movecharged particles through an opposing electrostatic field. Moving acharged particle against a force gradient in an electrostatic fieldrequires work. The work performed on the particle is converted into anincrease in the field strength. More particularly, an ionic species,such as a positive ion, may be acted upon by the wind in an inducedelectrostatic field. The molecules of the wind collide with the chargedion and do work on it, causing it to move in a direction against theforce imposed by the field. Consequently, the electric field strength(expressed as volts/meter) increases to a stable operating level. If theelectric field is between two collectors, e.g., porous plates, meshes,or other conducting objects, the movement of charge induces its ownfield, and one collector becomes negative with respect to the other. Aswind continues to drive the supplied stream of ions against the inducedfield, the voltage between the two collectors continues to climb. Theelectrostatic field strength stabilizes, and the work of the wind on theparticles may be used to separate particles of opposing charges, entrainone species of charge, and convert the other, orphaned into an electriccurrent. If the two collectors are electrically connected together, thecurrent flows between them as a result of the difference in potential.If an electrical load is placed in series with the collectors, usefulwork may be performed. The complete electrical circuit is thus composedof the ion current, the positive collector current, the return current(which may include the ground), the load current, and the negativecollector current.

The efficiency of an EHD wind-energy conversion system may be dependenton the ability of the wind to increasingly separate positive fromnegative charges. In terms of the physics, the wind force (in Newtons)on a water droplet can be described by the Stokes equation for laminarflow:F _(d)=6×π×η×v×r,  (1)where η is the viscosity of the air, v is the relative velocity of windwith respect to a particle, and r is the radius of the droplet of water.Electrostatic force (in Newtons) is a function of the number of coulombsperched on the droplet, and the strength of the electrostatic field inwhich it is moving:F _(e) =Q×∈,  (2)where Q is coulombs of charge and ∈=electric field (volts/meter).

The relative velocity of the wind with respect to a water droplet isdetermined by the force balance between drag force and electric fieldforce. At steady state, those forces are in balance (i.e., equal) andthe droplet is held immobile between the two opposing forces. EHDdepends on the ability of the wind to push a droplet against theopposing electric field, thus performing work on the droplet. Aneffective EHD system allows the droplets to be pushed through the fieldat some optimum velocity appropriate to the wind and atmosphericconditions. During stable power output, the drag force on a waterdroplet is substantially equal to the electric field force on the waterdroplet (e.g., the system is in a steady state).

For a given wind speed, there is a droplet size, droplet charge, andfield strength that extracts the maximum amount of wind energy. Adroplet may be as small as possible to maximize its charge-to-massratio, but is also, in one embodiment, at least large enough to keepfrom evaporating before it completes its system circuit. In anotherembodiment, the droplet contains a solid material, or a material thatbecomes a solid when the droplet evaporates, which inherits the chargeof the droplet, as explained further below.

One method of producing charged water droplets utilizes an electrosprayprocess. The amount of charge on a droplet is determined by theefficiency of the electro spray process, with 70% of the charge limit asa typical number. Beyond the charge limit, more charge on the surface ofthe droplet causes the droplet to explode in what is called a “Coulombicexplosion.” The size of the droplet is determined by a set of factorsrelated to the electrospray process itself, but in general is a functionof nozzle geometry, electric field strength in the vicinity of thenozzle tip, and the fluid pressure.

The droplet begins to evaporate as it leaves the nozzle. Evaporationrate is a function of temperature, pressure, and relative humidity (RH).RH is itself a function of the number of other droplets evaporating inthe vicinity of the process from other nozzles.

The higher the collecting electrostatic field strength, the lower theoutput current is to collect wind energy. Simultaneously, the higher thefield strength, the less charge is put into the air. The higher thefield strength, however, the more the droplets tend to be driven back totheir source nozzles. Thus, every wind speed and set of operationalconditions has a maximum applied electrostatic collection field thatpermits operation. There is also an optimum field that permitscollection of the maximum amount of energy.

Using standard sensors that provide information about incoming windspeed, air temperature, relative humidity, and pressure, we establish anEHD droplet and electric-field profile that extracts the maximum amountof energy from the wind. Operational parameters are sensed and adjustedin real-time. The system can be computer controlled, thus automatingboth fine and gross adjustments of key system parameters.

In addition, increasing or decreasing the CO₂ concentration in water isa means of altering pH and conductivity. For example, to increase CO₂and lower pH, water may be trickled downward in a packed column whileair is blown upward. This technique may be used to modify feed water tooptimize energy generation.

In general, smaller charged particles are preferred. Unfortunately,liquid droplets on the order of 1 micron in diameter do not survive verylong. They evaporate, leaving highly mobile and consequently ineffectivefree charge behind. One way to address this is to ensure that anevaporating particle of water leaves behind a solid or low-volatilityliquid. Candidate solids include dust, pollen, manufactured items suchas polymer balls, or solids formed by the final evaporation of liquid,such as salt crystals. Candidate liquids can include light oils that canbe pre-agitated to droplets on the order of 0.1 to 0.01 microns indiameter, and uniformly mixed with water.

Electrospray ionization (“ESI”) works in the same fashion. A carrierfluid droplet is charged using electrospray, and the charge originallyon the fluid droplet is deposited on the contained molecules ofinterest. The same process works for other solid species. These chargedspecies are entrained in the wind just like their parent droplet. In oneembodiment, the carrier fluid (e.g. water) is seeded with a substanceintended to carry the system working charge once the carrier dropletshave fully evaporated.

In a related embodiment, the nozzles are placed such that electrospraydroplets encounter airborne particles after nozzle emission. Here, thecharged droplet attracts generally uncharged solid particles, such assoot, pollen, dust, and other similar airborne substances, and entrainsand absorbs them. The ultimate effect is the same as before, with thesolids acting as charge carriers once water has evaporated. Dropletswith contaminants, or residual charged contaminants, may be removedusing a downstream collection grid. Employment of a downstream grideffectively performs the function of an electrostatic dust precipitator.In urban settings, such a arrangement can serve the dual purposes ofenergy generation and air purification by particle removal.

In other embodiments, liquids other than water are used as thecharge-carrying fluid. Any fluid that can form electrospray is acandidate. There are classes of fluid, having low vapor pressure and lowvolatility, that may have fewer tendencies than water to evaporateduring the time span of energy collection. Such fluids have theadvantage that much smaller droplets may be employed without danger ofcomplete droplet evaporation and consequent release of free charge.

In one embodiment, the working fluid is environmentally friendly andbiodegradable. In other embodiments, the charge carriers are species ofmolecules that are beneficial to downwind elements. For example, atypical application might be to charge a type of fertilizer, so thatdownwind soil is fertilized.

One aspect of putting a cloud of charge into the air is that it createsa space charge that is self-repulsive. Like charges repel one anotherand a cloud of like charges is highly self repulsive. A space chargecloud wants to push itself apart, but it also resists a like chargebeing pushed into it. This is the situation with EHD particles. Aparticle exits a nozzle and immediately is pushed by the wind towardsthe cloud of charge immediately downwind.

The nominal field strength from space charge in the shape of an infinitewall is described by the following formula:E=ρL/2∈,  (3)where E is the space charge field [Volts/meter] at entry to charge wall,ρ is the charge density (coulombs of charge per cubic meter), L is thethickness of the charge wall, and ∈ is the universal permittivityconstant of space (i.e., 8.85E-12 Coulombs²/(Nm²)).

Geometrical aspects of the space charge field may influence itsstrength. For instance, space charge in the shape of a cylinder, ratherthan a wall, has a weaker induced electric field than a wall of charge.A flat sheet of charge, such as one that might be emitted from a singleline of nozzles, may have an even lower space charge.

Space charge may be taken into account along with the other systemvariables such as wind speed, particle size and charge, and relativehumidity (natural and induced), among others. The charge density may becontrolled to account for the space charge effect. In one embodiment,control is modulated in real-time by a computer which examines allsystem parameters through the use of sensors and takes appropriatesystem action in order to optimize energy output for a given wind speedor other local environmental condition.

Space charge is directly proportional to the quantity of a specificcharge, plus or minus. If plus and minus charges are mixed together,they effectively neutralize, and space charge is lessened or eliminated.In one embodiment, a nozzle configuration alternates nozzles or rows ofnozzles that put out, alternately, positive and negative charges. Poweris still generated by employing the standard EHD model described herein;however, as the opposing charges mingle, their charges are neutralizedand space charge is minimized or eliminated. Such a space chargereduction enables more efficient wind energy collection by enabling theemployment of higher charge density without the penalty of the spacecharge.

There are two electrostatic fields fundamental to EHD operation. Onefield, the electro spray field, surrounds each electro spray orifice;the other field, the collection field, opposes the motion of droplets inthe wind. While these fields do indeed interact with one another, forthe purpose of control we can treat them separately.

A strong collection field implies a high collection voltage. Fieldstrength (volts/meter) depends in part on the physical relationship ofupwind voltage and a downwind charge collection grid. For instance, anozzle array operating at −200 kV with a grounded collection grid onemeter away from the nozzles would have a nominal collection field of 200kV/meter. The space charge field is added to the collection field todescribe the total field that a particle experiences when passing intoand through the collection zone between nozzle and downwind grid. In oneembodiment, a downwind collector grid employs adjustable spacing betweenitself and the electrospray nozzles (upwind grid) to advantageouslyconfigure itself to an optimal distance.

For water flow rates per nozzle that are sufficiently low, as whendroplet sizes are small and charge per unit mass is high, atmosphericcondensation of water may be used as a water source for the EHD process.It takes energy to condense water from the air; this condensation energymust be subtracted from the total energy output. Under favorableconditions, however, such as high humidity and moderate temperatures,condensation may be used advantageously.

Condensation energy may be minimized by utilizing an air-to-air heatexchanger. Moisture-laden air coming into the condenser may be cooled bydrier air exiting. Although there may be an enthalpy mismatch betweenthe air streams, and incoming air may not be fully cooled, energysavings may be significant.

Condensation for water supply may be exploited anywhere, thus providingmore freedom in system citing. Locations for condensation-suppliedsystems include sites with no local or municipal water, and airbornesystems.

FIG. 1 illustrates one embodiment of an EHD energy capture system 100. Acharge generator 102 creates a number of particles 104, which may beions, water droplets, or other suitable charge-carrying particles,thereby creating a space charge 106. The space charge 106 is porous tothe wind 108 that blows through and among the charged particles 104,driving them by hydrodynamic coupling in a direction generally the sameas the wind direction. A first, upstream charged mesh 110, porous to thewind, is charged with a polarity opposite to the space charge 106. Asthe particles 104 are driven away from the upstream charged mesh 110,the voltage of the upstream charged mesh 110 is maintained by a voltageregulation circuit 112 with respect to a second, downstream charged mesh114 that collects the charged particles 104. In some embodiments, asexplained further below, the downstream mesh 114 may be eliminated, andits function replaced by ground or by charge recombination in thedownstream air. As work is performed on the particles 104 by the wind108, excess positive charge near the downstream collector 114 pullsnegative charges from the upstream collector 110. The voltage regulator112 bleeds electrons from the upstream mesh 110 to maintain a constantvoltage. The current formed by the flow of electrons may be passedthrough a load 116 to perform useful work. In one embodiment, thecreation of a positive ion at the charge generator 102 simultaneouslycreates an electron. The electron travels from the upstream collector110 and moves through the load 116 to meet back up with its mate on thedownstream mesh 114.

FIG. 2 illustrates an alternative embodiment of an EHD energy capturesystem 200 that separates the ion source 202 from the EHD power circuit.In this embodiment, the ion source 202 provides one species of ion 204for use in the space charge field 206, and grounds the oppositelycharged ions 208 thereby generated. As the working ions 204 are blown bythe wind 210 into the space charge 206 between the upstream anddownstream collectors 212, 214, an electrostatic field 216 is induced,and the downstream collector plate 214 collects the charges 204. The ionsource 202 may be a corona-wire ion source, the voltage of which may bedecoupled from the voltage of the upstream collector 212.

The corona effect ion source 202 may be electrically separated from thespace charge 206 portion of the system 200. The counter ions 208 createdby the ion source 202 are drained to ground where they may be availableto the upstream and downstream collectors 212, 214. With the downstreamcollector 214 connected to ground 218 and the upstream collector 212connected to a load 220, both collectors 212, 214 may interact withelectrons from ground. The space charge 206 and the motion 222 of thecharged particles 204 against the electrostatic field 216 may induce anegative voltage in the upstream collector 212. The negative bias of theupstream collector 212 may be held at working voltage by a voltagecontroller/regulator 224. The current that flows through the controller224 may be harnessed at the load 220 to perform useful work.

In one embodiment, the original charge that begins driving the processis provided by a power supply 226 in the ion source 202. In anotherembodiment, stored or outside energy is used to power up the system 200.Once in progress, wind-derived electrical energy may be bledparasitically from the main system to power the ion source 202. In someembodiments, the ions 204 may be created at the ion source 202 andtransported to a distal location using, for example, a tube or pipeconstructed of, e.g., plastic or metal. The tube may have electrosprayorifices along its length. Such an arrangement may be advantageous forweight reduction in systems where, for example, a heavy wave guide isundesirable.

In other embodiments, the ion source 202 is an electrospray generator,an electron-cyclotron resonance (“ECR”) ion generator (powered bymicrowaves), a helicon ion generator, and/or an inductively-coupled iongenerator. In one embodiment, air itself is the ion source and the bulkmedia. An ECR ion generator, in comparison to a corona-effect iongenerator, can have higher energy efficiency (expressed in coulombs ofion charge per energy input, or C/W), higher conversion efficiency(expressed in moles of target ion species created per mole of availableneutral species, or moles/mole), and proportional control over a widerpower band. ECR ion generation thus enables energy extraction from windat lower wind speeds than those required by corona-based orwater-droplet-based systems.

At lower wind speeds, the upstream collector 212 voltage may be loweredto prevent the ions 204 from drifting backward due to ion mobility inthe lower electrostatic field. The minimum or “cut-in” wind velocity maybe arbitrarily low, thus capturing wind energy at speeds comparable toor lower than those required by conventional wind turbines. Typicalcut-in speeds for conventional wind turbines are around 8 mph (3.6 m/s).At low wind speeds, the EHD energy capture system may capturesignificantly more wind energy than a conventional wind turbine.

Proportional control of the ion source 202 over a broad range of ionoutput densities permits simultaneous optimization in coordination withthe controlled voltage of the collectors 212, 214. For a given windvelocity, there is corresponding collector voltage that creates asuitably high electric field so that energy may be captured, butsuitably low to prevent drawing back working ions due to charge mobilitywithin the field. Likewise, the ion density, which induces the electricfield, may be controllable within a range suitable for maximum energyextraction.

FIG. 3 illustrates one embodiment of an EHD energy capture system 300having a single collector 302. An electrically neutral fluid, havingequal numbers of positive and negative charges, is stored in a feedsource 304. At a charge separation point 306, positive charges aredeposited on charge carriers 308 which are carried away by the wind 310.Negative charges 310 are left behind on the collector 302. An electricfield 312 forms as a result of the force between the opposing charges.As more positive charges 308 are driven away by the wind, more negativecharges 310 are left behind, thereby increasing the strength of theelectric field 312 and creating a reservoir of charge that can bedrained off as current 314. If the electric field 312 becomes toostrong, however, it may overcome the force of the wind 310 on thepositive charges 308, and the charges 308 will not be blown away fromthe collector 302. Embodiments of this invention thus can be controlledto seek to maintain a steady-state balance, wherein the wind force isstrong enough to separate the charged particles from their source.

FIG. 4 illustrates one embodiment of an EHD system 400 that useselectrospray nozzles 402. The electrospray nozzles 402 may be filledwith a working fluid 404 that is maintained at a given pressure by, forexample, pumping the fluid 404 from a suitable fluid supply reservoir orreceiving the fluid 404 from a pressurized source. An electrosprayvoltage V_(es) and an electrospray current i_(es) are applied to thenozzles 402 to create electrospray. In one embodiment, the electrosprayvoltage V_(es) is approximately equal to 5 kV and the electrospraycurrent i_(es) is approximately equal to 200 nA. The electrospraycurrent i_(es) and voltage V_(es) may be supplied by an electrospraypower supply 406 that, in one embodiment, derives its power from theoutput of the EHD system 400 itself. When the EHD system 400 starts up,the power supply 406 may employ energy stored from prior output to startthe system 400.

Charged droplets 408 are created by the electrospray and may be emittedfrom the upstream collector 410 as a generally continuous plume ofcharge. The upstream collector 410 may be a screen or mesh grid, theelectrospray nozzles 402, or any other charge-bearing material near theelectrospray 408. In various embodiments, the droplets 408 arepositively or negatively charged. The droplets 408 are entrained by thewind in 412 and may be carried into an electric field 414. The electricfield 414 is defined by (1) the voltage difference between a systemvoltage V_(sys) on the upstream collector 410 and a downstream collectorand ground 416, and (2) the distance D between the two collectors 410,416. For example, in one embodiment, V_(sys) is 100 kV, ground is 0 V,and the grid spacing D is 0.5 meters. The electric field 414 willtherefore have a strength of 100,000/(½)=200,000 volts/meter.

The system voltage V_(sys) is created by negative charges, e.g.,electrons, left behind by the positively charged fluid droplets 408. Thesystem 400 may also operate by creating negative droplets, therebyleaving behind positive charges on the upstream collector 410. The moreelectrons left behind, the greater the negative voltage drop on thesystem voltage V_(sys), and the greater the strength of the electricfield 414. For any given wind conditions (e.g., speed and/or direction),a certain amount of drag is available to carry the charged droplets 408through the electric field 414. Thus, a balance between wind speed andelectric field strength determines the optimal operating point of thesystem 400. The strength of the electric field 414 may be varied byadding more droplets 408 per unit time and/or varying the charge perdroplet 408.

Once the system voltage V_(sys) achieves a steady-state value, electronsleft behind by the electrospray may form a current i_(sys) and flow viaa path 418 through a transformer 420. In one embodiment, the output fromthe system 400 is high voltage and low current. Output from thetransformer 420 will typically be lower voltage and higher current,thereby matching the requirements of a particular load 422. The loadvoltage V_(load) and the load current I_(load) are, in one embodiment,approximately equal to 115 VAC and 30 Amps, respectively, matching therequirements of a household power supply.

Under steady-state conditions, the flow 418 of electrons from theupstream collector 410 is equal to the positive charge flow carried onthe positively charged droplets 408. This overall system current 424 mayalso be equal to the ground current 426 (i_(ground)) that neutralizesincoming positive charges 408 at the downstream collector 416. Note thatcurrent may alternatively be defined in the direction of electron flowor opposite the direction of electron flow.

In one embodiment, the downstream collector 416 is removed from thesystem 400, leaving only the upstream collector 410. Instead of adownstream collector, the system 400 may use any electrical ground as apool of free charges. In one embodiment, the electrical ground is theEarth. The upstream collector 410 may be conductive and porous orforaminous. The upstream collector 410 may create a capacitive couplewith the electrical ground.

Eliminating the downstream collector 416 may create a much larger lengthfor distribution of system voltage. For instance, if the nominaldistance between the upstream voltage and ground is 10 meters, then thesystem sees an applied voltage of 200 kV/10 m=20 kV/m field. At the sametime, the space charge field may not be bounded by the downwind grid,and it increases linearly with the thickness of the space charge.Elimination of the downstream collector 416 may be best suited forsystems where the energy output is not space-charge limited.

In one embodiment, the system 400 includes a sensor 428 that measuresambient atmospheric parameters such as wind speed, temperature,humidity, as well as internal parameters like the strength of theelectric field 414. A control system 430 may communicate with the sensor428 and alter a parameter of the system 400 in response to the receivedsensor 428 data. For example, the control system 430 may modify the rateof creation of the charged particles 408 and/or vary the amount ofcharge on each particle 408 in response to a changed atmosphericparameter. The control system 430 may include a local computingdevice/processor or a remote device/processor, and may receive data fromthe sensor 428, process it, and adjust a parameter of the system 400 inreal-time. The control system 430 may be programmed with a look-up tableof recommended system 400 parameters for a given set of atmosphericconditions, and/or may determine optimal parameters throughexperimentation and feedback. For example, if the velocity of the wind412 increases, the control system 430 may raise V_(sys) and/or i_(sys)in response. In some embodiments, the control system 430 increases theflow rate of the charged particles 408 in response to increasing windspeeds, particularly if the increased wind speed is less than about 25mph. In other embodiments, the control system 430 raises the amount ofcharge per particle 508 with increasing wind speed (and a correspondingincrease in wind drag per particle to support the increased charge). Thecontrol system 430 may also increase particle size and decrease chargeper particle as wind speed increases, to take advantage of the increasedwind drag, or decrease particle size as humidity increases to takeadvantage of the slower rate of evaporation. The control system 430 maytake similar but opposite actions when wind speed decreases.

Diffuser Augmentation

FIG. 5 illustrates a cross-sectional cutaway view of one embodiment of adiffuser 500 for increasing the flow velocity and mass flow rate througha specific area of an EHD system called diffuser augmentation (“DA”). DAmay use a shaped structure to force a large cross-sectional area of windflow into a cross-sectional smaller area, thus causing an increase inthe wind's velocity in the smaller area. Higher-velocity wind flow maybe advantageous to charged-particle entrainment and drag forces againstwhich the electric field is applied, and may allow a stronger electricfield than would otherwise be possible.

Charged particles are entrained in the enhanced wind and create a spacecharge, per prior discussion, in a constrained and controlled spacedefined by the diffuser 500. In the diffuser 500, radial expansion ofthe wind is constrained by the walls of the diffuser 500. In oneembodiment, the walls of the diffuser 500 are charged to repel the spacecharge. Expansion of the space charge may prevent separation of flowfrom the diffuser wall as mass flows towards a downstream collector 514.As before, a voltage field is set up between the upstream and downstreamcollectors 508, 514. Electrically connecting the collectors 508, 514creates a circuit from which energy may be extracted.

The diffuser 500 is one embodiment of a radially symmetric DA-EHDdevice. A region 502 of ambient air outside of the diffuser 500 has abulk wind velocity V₀. As the ambient air encounters the intake zone504, it assumes a new velocity V₁ in accordance with the shape of theintake zone 504. The air within the intake zone 504 is accelerated to anew velocity V₂ as it moves toward the throat area 506, and experiencesa commensurate drop in pressure in accordance with Bernoulli's law. Atthe throat 506, the wind moves through an upstream collector 508, andcharged particles are injected into the wind by a distributor 510. Theparticles may be water droplets, charged dust, or simply charged speciesof air molecules. From the distributor 508, a space charge is created bythe moving cloud of charge. By the nature of the diffuser, and becausethe space charge naturally wants to expand, pressure increases andvelocity decreases as flow moves toward the exit 512 of the system. Thewind passes through a downstream collector 514 with a correspondinglower velocity V₃. In one embodiment, the upstream collector 508 is aconductive ring around the high-velocity zone, thereby allowing forsmoother flow of wind through the throat 506.

The ratio of the cross-sectional area of the exit 512 to the throat 506may be less than approximately 4.5. The velocity V₂ of the wind in thethroat 506 may be approximately equal to twice the ambient wind speedV₀, and the velocity V₃ of the wind at the exit 514 may be approximatelyequal to one-third of the ambient wind speed V₀. Other geometries andvalues are contemplated.

FIG. 6 illustrates a partial sectional view of one embodiment of alinear DA-EHD housing 600. Ambient wind enters the linear diffuser 600at an intake zone 602, accelerates at a throat 604, and leaves at anexit 606. An upstream collector and distributor may be positioned nearthe throat 604, and a downstream collector may be positioned near theexit 606. The linear diffuser 600 may be arbitrarily long about itslongitudinal axis 608, and may be mounted on, for example, hill tops,buildings, and the like.

FIGS. 7A-7B illustrate one embodiment of a DA-EHD balloon diffuser 700.The balloon diffuser 700 includes a balloon 702 and a duct 704 thatsurrounds the balloon 702. The front area 706 of the balloon 702 may actas an upstream collector, and the air flow may be driven into theboundary layer 708 that surrounds the flow-enhanced circumference. Theduct 704 may be constructed of a light frame with fabric stretchedbetween, and the balloon 702 may be constructed of a suitableair-impermeable membrane and filled with an appropriate gas. The balloondiffuser 700 may be used with either an air-based or awater-particle-based EHD system. In one embodiment, the balloon diffuser700 is positioned within a cloud. The balloon diffuser may also includelifting elements, such as wing structures, to add lift to the overallstructure.

The DA systems illustrated in FIGS. 5-7B feature several advantages. Forexample, the DA systems permit capturing energy from the nominal intakearea and, in addition, the enhanced velocity at the throat permitshigher electric field strengths. Furthermore, due to the enclosed natureof the DA systems 500, 600, 700, the electric field may be bettercontrolled between the collectors. The ratio of downstream to upstreamcollector area may better match the aspect ratio of the electric field.Inside the DA systems, the space charge is radially or transverselyconstrained, so that natural internal repulsion adds to velocity in thedesired work direction. The diffuser sleeve prevents ionic species frommigrating in from the bulk flow and prevents charge neutralization. TheDA designs contemplated by the present invention may enhance EHD systemsthat use such charge carriers as plain air, charged dust, waterdroplets, or rigid foam balls. If a fluidic charge carrier is desired,the design may be adapted for closed-loop flow (by, e.g., waterrecycling). The DA systems may be adapted for lighter-than-airconfigurations.

Dielectric Barrier Discharge

In one embodiment, a dielectric barrier discharge (“DBD”) device is usedas an ion source to create charged species using air alone, with noseparate charge carrier. DBD may be combined with DA to create a DBD-DAEHD device that has no moving parts (other than the wind itself). DBDplasma conditions may be varied to promote creation of specific ionicspecies. For instance, by combining a voltage field transverse to the ACfield of the DBD, ions of specific charge may be extracted to eitherside of the dielectric plate(s). The ions may then be employed to createan entrained space charge and the oppositely charged collector.

DBD may also be employed to charge naturally occurring dust particles.These particles occur with great abundance in the atmosphere. Themobility of a dust particle may be less that that of an air molecule,while, at the same time, the dust particle may hold a large electriccharge.

An electric field transverse to the collector field lines may bemodulated to motivate a charged species transverse to the flow. An ionthus perturbed may experience more collisions with the wind per unittime, and may be further influenced by those collisions generallyopposite to the direction of the applied field. The ion's mobility iseffectively lowered by such a means. The advantage of slowing the ion'smobility is that higher field strengths may be employed for wind energyextraction, and thereby improve energy extraction efficiency.

Injection of Charged Water Droplets Using MEMS

In various embodiments, EHD systems may inject charged water dropletsinto the air using micro-electro-mechanical structures (“MEMS”) thatincorporate appropriate pressure, flow, and voltage conditions. Inparticular, MEMS-based ink jet spraying and electrospraying combinedroplet formation with droplet charging.

Ink-jet technology optionally employs piezoelectrical vibration to ejectink droplets from an orifice, and then adds charge to each droplet as itfinds its way to the print media. Conventional individual inkjetejectors, which may consume 0.5 μJoules of energy to create one droplet,may not be efficient enough for use in an EHD system. A system thatemploys 2D ejector arrays with resonant actuators, such as piezoelectriccrystal or capacitive actuators, may fire droplets from large arrays oforifices. For example, a 2D array may contain 20×20 holes, and may bedriven in excess of 1 Mhz. As one example, the energy per droplet usinga single ethyl alcohol reservoir micromachined ejector array is 0.0037μJoules. Water energy per drop is deemed to be similar. Furtheroptimization of the MEMS devices may bring this energy figure down evenfurther.

Similarly, electrospraying induces a charged droplet stream from a smallnozzle with little significant pumping energy other than an appliedelectric field. Electrospray ionization (“ESI”) is a process of specialinterest to EHD systems. ESI may be deployed at the microscale usingMEMS technology to combine the creation of energy-efficient ultrasonicdroplets with electrostatic charging. In various embodiments, a MEMSejector reservoir array may be combined with a voltage source, thuscreating an energy-efficient electrospray device having a large numberof ejector nozzles. Besides creating the droplet itself, additionalenergy may be required to charge the droplet, to remove particles thatmight clog the micro-nozzles, and to move the fluid around from sourceto nozzle. Energy requirements for these processes are small compared todroplet creation energy and related inefficiencies.

FIG. 8 illustrates one embodiment of a MEMS charged-particle source 800that combines an ejector reservoir 802 with a porous charge plate 804. Anozzle plate 806, separated from the charge plate 804 by a distance D₂,may be charged to the same potential as the desired charge of a droplet808, for example, to 1 kV. The charge plate 804 may be biased at apotential opposite to the potential of the nozzle plate, for example, at−5 kV. In an alternative embodiment, the charge plate 804 may be set toa positive voltage and the nozzle plate 806 to a negative voltage. Inone embodiment, the potential of the charge plate 804 is the same as thepotential of an upstream collector. The fluid in the reservoir 802 neara nozzle 808 acquires the same potential as that of the nozzle plate806. The charge plate 804, being set to an opposite potential, attractsthe fluid away from the reservoir 802. The fluid may exit the reservoir802 and form a charged droplet 810. The wind 812, which may beperpendicular to the surface of the reservoir 802 and charge plate 804,entrains the droplet 810 carries it to a new position 814.

In one embodiment, the fluid in the reservoir 802 forms a Taylor cone816 before separating to form a droplet 810. The size of the nozzle 808,the distance D₂, and the potentials on the plates 804, 806 may all playa role in determining the particular mode of the Taylor cone. In variousembodiments, the source 800 is designed to have stable Taylor cones thatemit droplets 810 at regular and repeatable intervals.

In one embodiment, the droplet 810 is drawn at high velocity toward thecharge plate 804, but, because there is a hole 818 immediately oppositethe nozzle 808, the droplet 810 passes through and is entrained in thebulk wind flow 812.

In an alternative embodiment, charged particles are injected directlyinto the wind stream 812 without the use of the charging plate 804. Inthis embodiment, an actuator 820 may be used to provide energy to thefluid in the reservoir 802. The actuator may also be used in conjunctionwith the charging plate 804.

In one embodiment, the diameter of the nozzle 808 is on the order of thediameter of the droplet 810, which may be between 3 and 10 microns. Inother embodiments, the Taylor cone 816 may enable the production ofdroplets 810 that are smaller than the diameter of the nozzle 808, suchas, for example, sub-micron-sized droplets.

Charging the droplets 810 to a potential close to their Rayleigh limitcharge may have additional benefits. For example, when a charged droplet810 begins to evaporate in the bulk flow 812, the charge on the dropletapproaches its Rayleigh limit. Once the limit is achieved, the dropletmay break apart into smaller charged droplets in a process called aCoulombic explosion.

FIG. 9 illustrates one embodiment of a nozzle configuration 900. Anozzle 902 is formed on a substrate 903 and may be surrounded by agenerally annular channel 904, thereby forming a depression around thenozzle 902. The channel 904 isolates the nozzle 902 from the generallyplanar substrate 903 and can aid in the formation of a Taylor cone 906.

FIG. 10 illustrates an alternative embodiment 1000 in which a raisedzone or “scarf” 1002 is created on a substrate 1003 around a nozzle1004. The scarf 1002 may include material removed during the formationof the nozzle 1004, and may be a natural byproduct of non-volatilizedmaterial removal.

In an alternative embodiment, pre-existing hypodermic tubing orpre-shaped electrospray elements such as those fabricated by Phoenix S&Tof Chester, Pa. may be used.

In general, electrospray nozzle performance may be position dependent.For example, facing a nozzle downward may allow gravity to assist information of a Taylor cone. The nozzle may be faced in any direction,however, and still perform its function. The nozzle itself may take avariety of forms, including both single and ganged approaches. A gangedapproach is exemplified by any cluster of ordered nozzles that form partor whole sections of electrospray nozzles.

Electrospray System

FIGS. 10-19 illustrate, in various embodiments, an EHD electrospraysystem. FIG. 11 illustrates a structure 1100 that includes an extrusionbody 1102, a fluid channel 1104, and electrospray nozzles 1106 withinelectrospray clearance holes 1108. The electrospray nozzles 1106 may bepart of the plastic extrusion body 1102 that also includes somepost-extrusion processing. The extrusion body 1102 includes an airfoilshape, which may minimize turbulent losses at the nozzle array. Theairfoil shape may also permit control of high- and low-pressure areassuitable for various system processes. For example, the low pressurearea above and below an airfoil-shaped extrusion body 1102 may be suitedto injection of an electrospray plume. Entrainment air may optionally betaken in from holes at the leading edge of the airfoil-shaped body 1102,and/or the vapor pressure of the plume itself may be employed. The fluidchannel 1104 may run the length of the extrusion body 1102 and may feedthe nozzles 1106. The clearance holes 1108 may permit the electrosprayemanating from the nozzles 1106 to be entrained in passing air. Thenozzles 1106 point substantially transverse to the chord of theairfoil-shaped body 1102. In other embodiments, the nozzles 1106 aresuitably arranged to point in any direction as established by thegeometry of the fluid channel 1104, nozzles 1106, and appropriateclearance areas 1108. The body 1102 may alternatively be a roll-formedshape, or some combination of a roll-formed shape and an extrusion body.Materials other than plastics are contemplated.

FIG. 12 is a transparent view of an extrusion body 1200, showingadditional extrusion elements such as those inserted post extrusion orthat are co-extruded. The fluid feed channel accepts insertion of ahigh-voltage electrode wire 1202 that provides power (current andvoltage) to the electrospray fluid. Current from the wire may travelthrough the fluid to the tip of each nozzle and may be substantiallydistributed as charge on exiting droplets. Low-voltage electrode wires1204, here shown as co-extrusions, provide a proper electric field ateach nozzle top so that electrospray may occur.

FIG. 13 is an enlarged, transparent view of an extrusion body 1300. Thefluid channel 1302 of the electrospray nozzle 1304 intersects the mainfluid channel 1306. High-voltage 1308 and low-voltage 1310 electrodesare also depicted. The nozzle 1304 may be formed directly from theextrusion body material or may be formed by insertion and/or assembly ofa complete nozzle into a receptive cavity in the extrusion body 1300.Such an element might be a stainless steel needle or a plastic needlewith dimensions that rise above the contour of the fluid feed channel.

FIG. 14 is an enlarged view of a single nozzle 1400. The nozzle fluidchannel 1402 communicates with the feed channel 1404. A relief area 1406encircles and defines the orifice 1408 of the nozzle 1400. Nozzles 1400may be defined by first creating a nozzle fluid channel 1402 and thencreating the relief area 1406 around the channel 1402. Laser ablation isone process that is suitable for details of this scale and accuracy.

In various embodiments, the nozzle 1400 is constructed from a variety ofdifferent components and materials. It may be, for example, a metalneedle, such as those produced by New Objective, Inc., of Woburn, Mass.;a plastic cone, such as those produced by Phoenix S&T of Chester, Pa.; aplastic tip, such as those produced by Terronics Development of Elwood,Ind.; a MEMS-type nozzle, such as those produced by Advion, Inc. ofIthaca, N.Y.; a MEMS-type electrospray from sharp tips, e.g., “pencilsand volcanoes”; an orifice punched in continuous length fabricationssuch as extrusions, roll formed metals, or tubes; an orifice formed byinserting a custom feature into continuous length fabrications; and/oran integrated spray atomizer, such as Spray Triode from ZYW Corporationof Princeton Junction, N.J.

FIGS. 15 and 16 illustrate a full view of a louver 1500, which may besimilar to the extrusion bodies described above, and a louver array1600. The louver array 1600 is one example of how EHD wind energyconversion may employ one or more electrospray elements, e.g., louvers1500. The louver array 1600 may have a combined output of approximately5 kW. While the array 1600 may be substantially vertical, it isunderstood that the louvers 1500 may be staggered to provide better freeflow from downward-facing nozzles. An array with nozzles directedrearward or forward may be arranged in a similar fashion as the array1600.

FIG. 17 is an enlarged view of a portion of a louver array 1700. Theends 1702 of each louver 1704 may be open to provide sealing andfastening points for proper fluid, electrical, and mechanicalconnections. The connections may typically be established with avertical frame element.

FIG. 18 illustrates a framed louver array 1800. Rigid frame elements1802 constrain and support the louver array elements 1804. The frameelements 1802 may also provide the appropriate fluid connections for theelectrospray as well as electrical contacts for high- and low-voltageelements. The fluid elements may include pressure and flow control. Theelectrical elements may provide voltage and current control. Controlelements such sensors, pumps, and power supplies may be either internalor external to the frame elements 1802.

FIG. 19 illustrates an EHD system 1900. The system 1900 includes anupstream louver array 1902, including electrospray elements, and adownstream collector grid 1904. The downstream collector 1904 may beconnected to ground. The spacing D₃ between the louver array 1902 andthe downstream grid 1904 may define the magnitude of the electric fieldbetween them.

FIG. 20 illustrates cross-sectional view of a louver array 2000 withcanted louvers 2002 vertically offset in a downstream direction. Nozzles2004 on the louvers 2002 face downward. Where nozzles are arranged alongan extrusion or louver, nozzles facing straight downward or upward mayspray a plume that contacts an adjacent louver. In various embodiments,the louvers 2002 may be offset to permit the electrospray plume 2006more room to be entrained by the wind 2008. This layout may allow thelouvers 2002 to be placed closer together than an array with avertically aligned layout. Alternatively, the louvers 2002 may bestaggered, in a zig-zag pattern, or any other layout that permitsrelatively close nesting while providing adequate plume and windinteraction.

FIG. 21 illustrates an injection system 2100 having an alternativeelectrode configuration. An asymmetric electrode 2102 is disposed closerto the wind 2104 than an electrospray nozzle 2106. Because theelectrospray nozzle 2106 is transverse to the wind 2104, droplet forcesmay be asymmetric with respect to the central spray axis 2108. Thisasymmetry may be exploited to keep droplets 2110 away from the electrode2102 by placing the electrode 2102 upwind from the nozzle 2106. Theelectrode 2102 may include one or more wires; a single wire may besufficient to create an electrospray field and a Taylor cone 2112 at thetip of the nozzle 2106. The wind 2104 may assist in preventing theelectrospray 2110 generated by the Taylor cone 2112 from shorting to theelectrode 2102. Wire symmetry is not required. In one embodiment, theelectrode 2102 is an asymmetric, coated wire with a current leakagepath. A small patch of removed insulation 2114 may help to preventcharge neutralization on the surface of the wire-type electrode 2102.

In another embodiment, at lower wind speeds where there is not enoughdrag to keep charged droplets away from the charging electrodes, it maybe advantageous to coat the bare electrode with a dielectric substancethat retards the short-circuiting of droplets. A too-thick coating,however, sustains electrospray only briefly before the coating becomescovered with neutralizing charge, thus eliminating the driving electricfield and shutting down the electrospray. A proper coating thicknessenables some current leakage from the ensconced wire, preventing fieldneutralization while at the same time providing sufficient barrier to acurrent short between spray source and electrode. Another means ofpreventing driving field shutdown when using coated wire is to provide asmall current leak path in the insulation. A small cutaway of insulatingbarrier provides a path for counter-ions to neutralize charge buildup onthe coating surface.

In another embodiment, control of a short circuit current to the nozzleelectrode may also be accomplished by a current regulating circuit. Acircuit of this type may replace or augment the current-limitingproperties of a coated wire or a coated wire with cutaway. A relatedmeans of controlling current leakage between electrode and nozzle is toemploy an ion permeable material as an electrode coating. To the extentthat permeability is regulated by membrane structure, the leakagecurrent may be modulated.

EHD Applications

EHD wind energy conversion may be limited by the amount of ions that canbe put into the air, not by fear of mechanical destruction, and thus maywithstand arbitrarily high wind speeds. An ion source may be sized tosuit expected wind conditions in order to optimize cost vs. energyoutput. Because wind speeds may increase logarithmically with altitude,the higher off the ground a wind system is mounted, the more energy itmay produce. EHD wind energy capture is well-suited to higher windspeeds, including those well above the normal cut-out or maximum powerspeeds of conventional turbines. In fact, an EHD system may be lifted toarbitrarily high altitudes to capture wind energy at velocity regimesnot generally suitable for safe conventional turbine operation.

Traditional determination of available wind energy applies to EHD windenergy conversion. Each charged particle acts like a small wind bucketas neutral wind molecules strike it and force the particle against theelectric field. Trillions of ions retard wind speed just like a windturbine blade as kinetic energy from the wind is converted intoelectrical energy. Therefore, maximum theoretical available energy (at100% machine efficiency) is determined by the traditional Betz' Law:Power available=( 16/27)×½×(air density)×(area)×(wind velocity)³  (4)

Modifications to this equation may provide more realistic results. Forexample, a charge space composed of positive ions may expand due tomutual charge repulsion. This expansion may cause the charge space tooccupy a larger swept area than just the collector. Conversely,collisions between neutral air molecules and the ions are not perfectlyelastic and thereby result in friction losses.

FIG. 22 illustrates one embodiment of a ground-level-mounted EHD system2200. Columnar ion sources 2202 provide (in this embodiment) positiveions, which may induce a voltage in a porous collector fence 2204. Eachcollector panel 2202 may have a height H₄ and a width W₄. Otherembodiments may have more or fewer ion sources 2202 and/or collectorfence panels 2204. The ions may be driven by the wind 2206 against thevoltage gradient created by the charge space 2208 between the fence 2204and ground 2210. The ions may return to ground 2210 to complete thevirtual circuit. The ion sources 2202 may be electrically isolated fromthe collector 2204 and may have their own ground 2212. The collector2204 may have no ground, per se, because its voltage is controlled by avoltage controller 2214. The controller 2214, which also may have itsown ground 2216, may also convert electron flow (current) from thecollector 2204 into a line voltage 2218. The collectors 2204 may beraised above ground level by distance D₄ to prevent shorting thecollector 2204 to ground 2212. Electrical isolation may protect thecollector voltages, which may reach several hundred kilovolts. DistanceD₄ may be increased to allow the collectors 2204 to be exposed to higheraverage wind velocities. In one embodiment, the collector 2204 is aporous, conductive fence, such as a chain-link fence, with an ion sourceand a means of conditioning the voltage and current induced in thefence.

FIG. 23 illustrates one embodiment of a tower-mounted EHD system 2300.In general, increased height implies increased wind speed, at leastbecause ground effects slow down the wind and rob it of energy. Given afirst wind velocity V₀ at a first height H₀, the new velocity V at asecond, higher height His:V=(H/H ₀)^(α) V ₀,  (5)where α is a wind shear exponent. Although the wind shear exponent mayvary with terrain, it is generally accepted to be 1/7 (0.143). Forexample, a velocity of 5 meters/second measured at a height of 3 metersis becomes 7.36 meters/second at a height of 150 meters. Furthermore,wind power increases as the cube of wind velocity (V³). Combining thetwo expressions, there may be twice as much wind energy available at 100feet above ground than there is at 20 feet above ground.

An ion source 2302 emits positive ions 2304 into the wind 2306, therebyinducing a voltage in a collector 2308 due to a space charge 2310. Theions may return to ground 2312. In the tower mount, the collector 2308may be placed on a pivot 2314 that permits the wind to push thecollector 2308 downwind from the tower 2316. The system 2300 may alsoinclude voltage conditioning and grounding means.

The height of the tower H₅ may be arbitrary. In one embodiment, H₅ isover 100 meters. Given that EHD systems have no moving parts, nogearbox, and no generator, the support tower 2316 may bear lesssignificantly weight than a conventional wind turbine tower, and thusmay be less massive for a given height. Maintenance may involve checkingthe cleanliness of the collector grid, the soundness of electricalconnections, and/or sensing the integrity of coordinated power andcontrol systems. The rotary bearings at the top of the tower may have tobe checked and lubricated. Larger systems may use a servo-motor to drivethe collector grid to the proper orientation or employ a tail sail toorient correctly to the collector 2308.

FIG. 24 illustrates a building-mounted EHD system 2400. A building 2402of height H₆ has EHD system collectors 2404 mounted on its roof. Iongenerators 2406 may be mounted on the corners of the building 2402, andcollector grids 2408 may be positioned parallel to the four outsidesurfaces of the building 2402. In operation, the wind may produceelectrical energy from the roof systems as follows. Wind passing aroundthe corners of the building 2402 may pick up ions, create a chargespace, and induce a voltage into the collectors grids 2408. Of concernis turbulent back-flow on the downwind walls of the building 2402 whichmay permit ions to rejoin the collector grids 2408 without experiencingthe effect of the wind. This effect may be minimized by placing thecollector grids 2408 remote from the mid-portions of the wall, i.e.,more near the corners of the building 2402. The collector grids 2408 mayalso be positioned to extend straight out from the corners, as shown bycollector grid 2410.

Other manmade structures, such as the roof peak of a home, mayexperience wind velocity magnification due to the slope of the roof.Such locations may be advantageous for installation of an EHD windenergy system. Such a system may have a collector that is long andnarrow to suit the high-energy ribbon of air flowing over the peak.

In one embodiment, an EHD system may be mounted on a flagpole. The lightweight of a simple, porous collector mesh may not cause undue stress onthe flagpole. It may be mounted on the top with, e.g., a gimbalcomparable to the tower-mounting scheme. Electronics could be placed atthe bottom of the pole.

In general, the dimensions of the collector area may not be strictlydefined. Unlike the strictly circular path of a horizontal axis, bladedwind turbine, or the columnar profile of a vertical axis Darrieus windturbine, an EHD system collector need only heed the geometricrequirements relative to a charge field. For example, the collector areamay be long and thin rather than square or round. This geometricflexibility permits integrative designs to take advantage of unique windflow characteristics, such as around the corners of high buildings. Italso provides some measure of artistic license to createaesthetically-pleasing designs.

In alternative embodiments, EHD systems may be mounted on naturalstructures such as trees, boulders, and/or mountains. For more delicatestructures such as trees, a small and/or lightweight EHD system may beused. On large, sturdy structures such as mountains, larger EHD systemsmay be used. Wind speed near the ground at the top of a mountain can bequite high. To capture this wind energy, in one embodiment, a fence-typesystem may be used. Because an EHD system may naturally producehigh-voltage DC power, transporting power long distances may be less ofan issue. In one embodiment, AC power is converted to DC power.

FIG. 25 illustrates one embodiment of a portion of a turbine-blade EHDsystem 2500. An existing, conventional wind turbine may benefit byintegrating an EHD system with the turbine blade. Current EHD designsmay enhance the efficiency of the conventional wind turbines, and newEHD designs may dispense with conventional wind turbine components, suchas the generator and, if employed, the gearbox. In one embodiment, anEHD system may be retrofit from a conventional wind turbine.

The airfoil 2502 may act as a mechanical wind-velocity enhancer. Theairfoil 2502 is driven by the natural or ambient wind 2504, as a bladeof a wind turbine may be driven. The airfoil 2502 experiences a relativeor induced wind 2506 affected by the motion of the airfoil 2502 throughthe air. A volume of charged particles 2508 may be created as anion-rich region by an ion generator 2510, such as an electrospraysource, a microwave Electron-Cyclotron Resonance (“ECR”) waveguide iongenerator, or other suitable ion source. Ions exit the ion generator2510 through a waveguide slot 2512 near the leading edge of the airfoil2502 and may be prevented from returning by paired magnets 2514 at theexit of the slot 2512 and/or by positive gas (i.e., air) flow out fromthe slot 2512. The charge space 2508 is porous to the induced wind 2506which blows through and among the charged particles, driving them byhydrodynamic coupling in a direction generally the same as the inducedwind 2506 direction. The charged particles are therefore moved in adirection opposite to the space charge electric field 2516 created bythe collector plate 2518 mounted near the trailing edge of the airfoil2502, which may be charged with a polarity opposite to the ion charge.As the ions are driven away from the collector plate 2518, the platevoltage may be maintained by a voltage regulator 2520 with respect toground 2522. As work is performed on the space charge 2508 by theinduced wind 2506, excess charge may be built up in the collector plate2518. The voltage regulator 2520 may bleed current from the collector2518 to maintain constant voltage. This current may be passed through aload 2524 to perform useful work.

The collector plate 2518 may be charged to higher voltage than collectorplates of non-airfoil systems, because ion mobility back to thecollector 2518 may be overcome by the higher relative wind 2506velocity. The volume of air passing the ion release zone may also beincreased, thereby releasing higher ion densities than in non-bladesystems.

The relative wind 2506 velocity over the aerodynamic surface of theairfoil 2502 is typically several multiples (e.g., 4× to 10×) of thebulk wind 2504 velocity. Airfoil shapes may be optimized for combined(mechanical wind plus EHD) energy extraction, or optimized for EHDalone. In one embodiment, an airfoil for EHD-only extraction may notrequire a central generator. Instead, the blades of the windmill freelyrotate about a generally passive axis and may extract energy from thewind at the blades themselves. Such an approach may be able to extractwind energy at wind speeds both lower and higher than conventional windturbines.

In addition, the placement of the collector plates 2518 and thecomponents 2510, 2512, 2514 that make up the ion generator is schematicand exemplary. Placement of the items may take a different form. Forinstance, the ion generator assembly 2510, 2514 may be placed at theroot of the blade, and the ions ported up the core of the blade andsuitably dispersed with respect to the collector plate 2518.Alternatively, the collector plate 2518 may be placed on the undersideof the blade, thereby reducing neutralization by proximal positive ions.In one embodiment, a series of collector fins is extended into the airstream to provide a higher collection surface.

Integration of an EHD system with an airfoil may benefit the efforts ofconventional wind turbine manufacturers, such as Sky Windpower Companyof Ramona, Calif. Their approach is to use autogyro rotation of liftblades to support a wind energy platform at height. The instantinvention may lower the weight for any existing design and therebyimprove energy conversion efficiency.

One embodiment of the airfoil-integrated EHD system design employs theairfoil on an aircraft. When the EHD system is deployed, it may act asan air brake. Ions seed the air behind the wing, the collector creates aspace charge, and the ions want to migrate back to the collector. Eachion acts like a micro air brake as it bounces against oncoming neutralair particles. As the ions are forced away from the wind by air flow,the collector registers high voltage; current drawn off from thecollector is stored onboard for use another time. Energy conservationand efficiency are important for nearly every kind of aircraft; an EHDsystem air brake is especially valuable for electrically poweredaircraft.

In various embodiments, EHD systems may be used with kite-based windenergy systems, which are being actively researched by such companies asMakani Power of Alameda, Calif. Sky Windpower also contemplates usingdevices to lift turbines and generators in the air without a tower.Replacing a standard generator system with an EHD system may increasetheir efficiency. Less energy is wasted on lift, and more converted toelectricity. Kite-based power generation may yield improved wind speedwith increased height. A kite can achieve great heights without a tower,and power may be conveyed along the kite tether.

The details of integrating an EHD system with a kite follow. In general,ions are introduced upstream of the kite's lifting surface, and one ormore of the kite lifting surfaces may be rendered conductive in order toact as a collector. Energy is conveyed to ground with a tensionedtether, and the collector voltage may be readily conditioned to whateverform is necessary. The tether may be reeled out from a spool thatconverts the imparted rotational energy by using it to power, forexample, an electrical generator. When the kite is reeled in, it mayreduce its wind profile and thereby allow the spool to consume lessenergy than was captured in the reeling-out step.

FIGS. 26A-B illustrate a lighter-than-air (“LTA”) EHD system 2600.Integration of EHD energy generation with an LTA vehicle may offer thesame advantages as a kite-based EHD system, namely, placing the EHDsystem at a height that captures more wind energy than it would on theground. Unlike a kite-based system, however, an LTA system may be sizedto very large dimensions and/or be deployed at very high altitudes. Inaddition, LTA systems that use conventional generators, such as thoseproduced by Magenn Power Inc. of Canada, may benefit from the inclusionof an EHD system.

FIG. 26A illustrates an LTA vessel 2602 that may be a pressurizedcontainer, such as a helium- or hydrogen-filled balloon or dirigible.The surface of the vessel 2602 may be semi-rigid and/or rigid atspecific attachment points. The vessel 2602 may be anchored to theground by a tether 2604 at a height H₇. An ion source 2604 may bepositioned circumferentially at the line of highest wind velocity, andions may be released into the wind flow 2606 to create a space charge.The collector may be disposed on the surface 2608 of the downwind end ofthe vessel 2602 and/or may be a porous net 2610 positioned near the ionrelease line 2604. The nominal displaced area of the system is thefront-on displaced area 2612 of the vessel 2602 that forces enhancedflow around the periphery. The area 2612 may be increased by addingcollector surfaces such as the porous net 2610. Conditioned power may bereturned to earth along an anchor cable 2614 and further conditioned bya regulator 2616 to a suitable line voltage and frequency. A liftingforce may be supplanted by wings 2618, which may improve the angle ofthe tether cable 2604 with respect to ground. As shown in thisembodiment, the wings 2618 form part of the secondary collector platesupport system. Negative ions, produced by the ion generator 2604, maybe injected into the downstream air to neutralize the positive ions. Thecounter-ion injection downstream may therefore complete the electricalcircuit at altitude rather than relying on a ground circuit. In oneembodiment, the downstream counter-ion injection system is a pipe 2620releasing electrons that neutralize the positive free ions 2622. FIG.26B illustrates a reduced-sized side view of the LTA vessel 2602.

LTA/EHD systems may be capable of reaching heights in excess of 30,000feet, which is high enough to be inside the jet stream and takeadvantage of its high wind speed (120 mph or greater) and constancy. Forexample, even accounting for lessened air density, a 120 mph air streammay theoretically yield approximately 24 kW per square meter. Forcomparison, typical wind speeds at sea level may yields only 0.109 kWper square meter.

In various embodiments, an LTA-based EHD system may be combined with akite-based system. For example, a kite-based system may use alighter-than-air portion to create slightly positive buoyancy. Such asystem may be easier to launch in quiescent low-level winds.

An LTA/EHD system may have less weight than a conventional high-altitudewind-energy-conversion system (WECS”). Conventional high-altitudesystems (such as LTA-only or airfoil-only systems) require liftingturbine blades (or equivalent), gearbox, and generator to the requiredheight and sending power back to ground. Because LTA/EHD systems may notrequire some or all of these components, their overall weight may bemuch lower. Furthermore, lift is fixed by the buoyancy of a solely-LTAdevice, and the angle of incidence of the tether with respect to groundis determined by the lift to drag ratio. Additionally, a fixed-lift LTAdevice heels as wind speed increases. An airfoil-only device requireswind of finite and significant velocity in order to launch from theground

FIG. 27 illustrates one embodiment of an LTA/EHD system 2700. An LTAstructure 2702 of conventional shape is combined with a rigid airfoil2704. The airfoil 2704 has a lift to drag ratio (“L/D”) characteristicof an efficient design. At the downwind end of the LTA structure 2702 isa turbine blade set 2706 linked to a gearbox 2708 that then communicatesthrough an internal shaft to a generator 2710 at the upwind end of thestructure 2702. The system 2700 is connected to ground 2712 through atether 2714 that may also communicate signals and power between thesystem 2700 and ground 2712.

As depicted, the turbine 2706 is at the aft end of the LTA structure2702. In other embodiments, single or multiple turbines may be placed atany of a variety of attachment points along the body of the LTAstructure 2702.

In addition, a plane of energy extraction may be provided by any devicethat extracts energy from the wind, and may be similarly placed at avariety of points on the body of the LTA structure 2702. For example,one or more WEC systems may be placed on the LTA structure 2702 todeploy charged water droplets in an electric field and convert windenergy directly to electrical energy. Larger WEC systems may supportmultiple planes of energy extraction.

Because the buoyant portion of the system 2700 is sufficient to lift itinto the air, the system 2700 may be deployed at zero wind velocity.Winds at higher altitudes are likely to be higher than winds at ground,not only because of wind shear, but also because obstructions such astrees, hills, and buildings tend to block wind at ground level. Oncelofted, the airfoil 2704 may provide additional lift.

FIG. 28 illustrates a cutaway view of an LTA system 2800, showing alightweight shaft 2802 connecting the gearbox 2708 to the generator2710. The airfoil 2704 has actuation means 2804 to adjust its angle ofattack 2806 with respect to the wind. The LTA structure 2702 has asteering means in the form of fins 2808 with flaps 2810 that may permitoptional positioning of the entire device. During operation, the airfoil2704 may be angled to provide the optimum amount of lift for a givenwind condition while the steering means on the LTA 2702 provides desiredpositioning. For example, lower wind speeds may require a higher angleof attack 2806 for the airfoil 2704. Turbulent wind, operation in thevicinity of natural or man-made structures, and/or the presence of otheraerostats may necessitate steering and stabilization facilitated by thesteering means. The control surfaces 2810 and the airfoil angle 2806 maybe controlled by an internal guidance system 2812 or manually from theground through a control line 2814 or wireless means. The guidancesystem 2812 may additionally be coordinated with adjacent structures2800 in a multiple-unit wind farm. In such a case, the structures 2800may be additionally fitted with location devices that mutuallycommunicate aerial position. Guidance systems 2812 within each unit mayemploy internal control means to safely position the multiple units 2800with respect to one another and to additionally provide positioning thatprovides maximized power output for the entire system. A winch 2816connected to a spool 2818 on the ground 2712 may permit reeling in thesystem 2800 during inclement weather, for maintenance, and/or to set theproper operating altitude.

In other embodiments, the airfoil 2704 is replaced with any of a varietyof structures with suitable L/D ratio, such as, kites, parasails,self-inflating soft airfoils, inflatable wings, fabric ultra-lightwings, and the like. The LTA structure 2702 may also be itself shapedlike an airfoil, and may include the improvements detailed below.

FIG. 29 illustrates a LTA system 2900 its relationships with lift 2901and drag 2903, 2905. The ratio of lift to drag is essentially equal tothe ratio of the height H₈ to the distance D₈ that the system 2900 isdownwind from its mooring point 2902. The system 2900 experiences bothdrag and lift at the same time. The LTA structure 2904 may provide nolift when facing the wind straight on, unless, for example, it has sometype of airfoil shape. In addition, the LTA structure 2904 may causesignificant drag in and near the plane of energy extraction. Combineddrag may cause the system 2900 to heel over as wind speed increases. Theairfoil 2906 has an L/D ratio that depends on angle of attack 2908,which may be controlled by the system 2900. Thus, as wind speedincreases and more lift is desired, the angle of attack 2908 of theairfoil 2906 may be changed to compensate for increased drag 2903, 2905.In addition, the angle of the LTA structure 2904 itself may be changedby the steering elements, thus additionally compensating forwind-induced drag effects. All in all, the integrated system iswell-prepared to handle a wide variety of wind speeds and destabilizingeffects while producing a maximum amount of electrical energy.

In order to optimize the safety and stability of the system 2900 andminimize its labor costs, the system 2900 may include a variety ofsensing and feedback means connected to one or more control computers.An inertial-gravimetric system with feedback to the control surfaces maybe able to maintain operational stability even under turbulentconditions. A wind-speed indicator may determine boundaries for safeoperation, and may automatically cause the system 2900 to be winched toground, or likewise, deployed.

The tether 2910 may contain signal means to enable communication betweenthe ground and the system 2900. Such communication may permit manualoperation of positioning, system monitoring and diagnosis, startup, andshutdown.

The tether 2910 may carry high-voltage, low-current power from thesystem 2900. A transformer and/or power conditioning system on theground 2912 may convert captured power to voltage, current, andwaveforms suitable for interfacing with ground loads or power grids.

Because the system 2900 has no tower, it has no overturning moment. Asimple attachment point for the ground-based deployment and retrievablesystem provides the necessary base. The base may be mobile, such a basemounted on a vehicle (e.g., a boat) or may mounted to an anchored,floating platform. An advantage of the anchored attachment means is thatthe depth of the anchor is of minor significance, being limited only bythe available length and strength of anchor line. Existing off-shorewind-energy-conversion systems, however, are depth-limited because theymust provide an underwater foundation to support a heavier-than-airconversion system.

FIG. 30 illustrates one embodiment of an off-shore installation 3000. Ananchor point 3002 beneath the water 3004 keeps the mounting buoy 3006from migrating. No deep foundation is required. As with land systems,the LTA system 3008 may be reeled in for servicing. The buoy 3006 may beconstructed to provide protection for the LTA system 3008 when it isreeled in during rough weather.

Conventional tower systems are heavy, difficult to transport,challenging and expensive to install, and inconvenient and somewhatunsafe to service and maintain. All these difficulties are avoided withthe system 3000 because it simply may be winched down to the ground forconvenient servicing. Further, the internal steering means may beemployed to create generally neutral buoyancy so that the buoy 3006 hasonly enough tension on the tether 3010 to maintain control. Thisapproach suggests that mechanical requirements for active deployment andretraction of the tether 3010 are kept within reasonable bounds, even inextreme wind speeds.

An additional feature of the system 3000 is that, by communicating withthe LTA system 3008 along the tether 3010, the buoy 3006 may sense itseffect on the height and stability of the LTA system 3008. Thus, thebuoy 3006, in combination with an automated retraction mechanism, maysuitably let out or retract the tether 3006 in order to compensate formotion caused by, e.g., waves or tides.

Given the need to keep a wind-energy-conversion system aloft for longperiods of time, as well as the tendency for lifting gas to leak out ofthe LTA volume, it is a further goal of embodiments of this invention tocompensate for such leakage by providing in-situ gas production or byfeeding gas in from the ground through the tether 3010. Helium is alimited resource and has some significant expense. In addition, there isnot a convenient means of extracting helium from the atmosphere. It isbetter to realize that an isolated, unmanned wind-energy-conversionsystem may be filled with hydrogen, or with a mixture of hydrogen andair. Hydrogen may be produced on-board by electrolyzing water from astored water supply. Alternatively, water may be extracted from theatmosphere using a small, lightweight condenser, and the condensed watermay then be electrolyzed into hydrogen and oxygen. Hydrogen producedtherein may be used to fill the LTA volume; oxygen is discarded.

FIG. 31A illustrates an EHD system 3100 that uses wind shear to harvestwind energy. Wind shear is defined as one layer of wind having adifferent velocity than that of an adjacent, second layer. The system3100 employs an air anchor 3102 disposed in a first wind layer 3104 thatis attached, via a cable 3106, to an LTA/EDA system 3108 disposed in asecond wind layer 3110. The velocities of the winds in the two layers3104, 3110 are assumed to be different. In one embodiment, the secondwind layer 3110 is the jet stream. More than one anchor 3102 may beused. The wind shear zone 3112 may enable the use of an air anchorbecause the lower air is so much slower than the upper air. Capturedenergy 3114 may be transmitted to the ground using a microwavetransmitter 3116. Both the anchor 3102 and the EHD/LTA system 3108 maygenerate power because both are moving with respect to their windresources.

FIG. 31B illustrates a high-altitude view of a continent-sizedcollection system 3150 composed of numerous mobile EHD/LTA units 3100.Detroit and New York are shown for scale. A unit 2700 entrained in ahigh-altitude wind current 3110, such as the jet stream, is carriedalong until it hits a suitable loop back point 3118. Here, the EHD/LTAsystem 3100 may exit the jet stream 3110 and return to a suitable entrypoint 3120, whereby the cycle may be repeated. Multiple units may beemployed in a continuous loop.

Powering an EHD/LTA unit 3100 from the exit 3118 to the entry point 3120may be accomplished by any of several means. For example, it may betowed by an aircraft or it may be powered by a thruster. A thruster maybe a propeller, a jet, or even an ion drive.

Embodiments of the present invention also encompass water-based energysystems. The use of a working fluid to separate charged particles in awork-capturing electrostatic field may also be applied to more viscousfluids such as water. A charge may be attached to a particle in much thesame way as it is attached to a water droplet. A positively chargedparticle will be attracted to its negative source, and the working fluidwill carry it away. Such a hydro-power application includes a means forcreating a positive and negative charge pair, and a means for placingone charge (or collection of them) on one carrier while the other isleft behind. As more charges leave on the carriers, more opposingcharges are left behind. More charge buildup results in a stronger andstronger electrostatic field. To extract energy, excess charge is bledoff through a load. Unlike air, which is an excellent insulator, waterwith even a small amount of dissolved solids or impurities has somelevel of conductivity. Free charge will flow through water like currentthrough a wire. Charge bound to a particle is able to be carried away bya current.

Because charged particle density can be fully controlled, even lowpressure heads such as that which can be found in un-dammed rivers andstreams may be used to push charge. Ocean currents, waves, tides, andstreams with low head may also be employed. Clearly, fluid systems withlarge working head will suffice as well.

Having described certain embodiments of the invention, it will beapparent to those of ordinary skill in the art that other embodimentsincorporating the concepts disclosed herein may be used withoutdeparting from the spirit and scope of the invention. Accordingly, thedescribed embodiments are to be considered in all respects as onlyillustrative and not restrictive and the various structures andfunctional features of the various embodiments may be combined invarious combinations and permutations. All such embodiments are to beconsidered as parts of the inventive contribution.

What is claimed is:
 1. A system for energy extraction from a fluid stream comprising: an emitter that emits a charged particle of a first polarity into the fluid stream; a sensor that monitors an ambient environmental condition; and a controller that adjusts a system parameter to increase energy extraction efficiency in response to a change in the ambient environmental condition.
 2. The system of claim 1, wherein the system further comprises a second emitter that emits charged particles of a second polarity into the fluid stream, wherein the second polarity opposes the first polarity.
 3. The system of claim 2, wherein the first and second emitters comprise a first and second nozzle, respectively.
 4. The system of claim 3, wherein the first and second nozzle are arranged in alternating rows.
 5. The system of claim 2, wherein the controller controls operation of the first and second emitters to alternate between emitting charged particles of the first polarity and emitting charged particles of the second polarity.
 6. The system of claim 5, wherein the controller controls the operation of the first and second emitters based on the ambient environmental condition.
 7. The system of claim 5, wherein the ambient environmental condition comprises space charge.
 8. The system of claim 7, wherein the adjusted system parameter comprises charge density.
 9. The system of claim 8, further comprising a second emitter that emits a charged particle of a second polarity opposing the first polarity into the fluid stream, wherein the controller adjusts charge density by controlling charged particle emission from the first and second emitters.
 10. The system of claim 2, wherein the system further comprises: a downstream collector that collects the charged particle; and a load electrically connected between the emitter and the downstream collector.
 11. A method for energy extraction from a fluid stream, comprising: emitting charged particles of a first polarity into the fluid stream; monitoring an environmental parameter; and changing a system parameter in response to changes in the environmental parameter to increase energy extraction efficiency.
 12. The method of claim 11 further comprising emitting charged particles of a second polarity into the fluid stream, the second polarity opposing the first polarity.
 13. The method of claim 12 further comprising alternating between emitting charged particles of the first polarity and emitting charged particles of the second polarity.
 14. The method of claim 11, wherein monitoring an environmental parameter comprises monitoring space charge.
 15. The method of claim 14, wherein changing a system parameter comprises changing a charge density of emitted charged particles.
 16. The method of claim 15, wherein changing a charge density of emitted charged particles comprises emitting charged particles of a second polarity into the fluid stream. 